The present invention relates to a new and improved method of, and apparatus for, applying a synthetic resin or plastic powder in the form of a grate-shaped or raster-shaped coating to web material.
In Swiss patent publication 8058/68 there is disclosed apparatus having relief-like structured printing rolls for application of a synthetic resin powder in a grate-shaped coating to web material and based upon such apparatus there is also discussed a method for coating textile supports or underlayers with pulverulent plastic or synthetic resin. With the aid of this known apparatus and while using the disclosed method there are particularly fabricated reinforcement inserts or linings for garments with a grate-shaped coating of a heat sealable adhesive. Generally, the heat sealable adhesive is applied to the insert in a point raster or grating configuration, the soft textile handle being retained in the composite consisting of the insert and the top cloth. With the teachings of the aforementioned Swiss patent publication it is not always possible to attain the aforementioned results, particularly if the corresponding requirements continuously become greater.
More promising is another coating technique which has become known from German petty patent 7,211,197 which consists of a grate-shaped lower layer of heat sealable adhesive having a high melting viscosity and/or high melting point or high melting range and only a second upper layer seated on the base grating or raster and of lower melting viscosity and/or lower melting point or melting range. The grate-shaped lower layer can be produced at the fabric web, among other things, with the aid of an engraving roller, and the adhesive formed of powder or paste can be squeegeed into the grate-like engraved portions of the roller and from there transferred to the material or fabric web. Prior to applying the upper layer the grate-shaped material piles of the lower layer are sintered so that upon applying the upper layer by means of a squeegee roll or a roll coater such functions in the manner of the type or lettering during relief printing processes and thereby is able to partially take-up by light contact the thin layer of a heat sealable adhesive applied to the smooth roller and which has been liquified by a plasticizer or under the action of heat. The lower layer is thus applied according to the manner of an intaglio printing process, possibly a silk screen printing process. It is then converted by sintering into a type of relief printing matrix and the application of the upper layer occurs in the same manner in which during relief printing the printing matrix is imbued with the printing ink. This is of course only then possible if the material piles possess adequate strength, that is to say, are practically hardened (the expression "sintering" is then also used in the aforementioned German petty patent apparently in this sense). Without fulfilling this condition the lower layer, upon application of the upper layer, automatically would be smudged or smeared. But even if the material piles of the lower layer are sufficiently hardened the aforementioned procedures remain cumbersome and with regard to their practical application extremely questionable. Producing a homogeneous thin layer of a heat sealable adhesive upon a squeegee roll is already difficulty, particularly due to temperature effects. However, an even greater problem is the need to insure that the thin layer is released from the squeegee roll by the depositions of the lower layer in all instances, but only by such depositions and not for instance also by the material web. Moreover, it probably will be impossible to avoid deposition of the material for the upper layer -- even if it can be released from the squeegee roll -- directly at the material web.